1. Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine, a printer, or a multifunctional peripheral, and a paper feeding device provided therein.
2. Description of the Related Art
There is a paper feeding device provided in an image forming apparatus, which sucks an uppermost paper of a plurality of papers stacked in a tray by a suction belt, and feeds the paper to an image forming unit. Among this type of paper feeding devices, one that feeds papers to the image forming unit of the image forming apparatus one by one at a high speed is known. An outline thereof is illustrated in FIG. 1.
In the paper feeding device of FIG. 1, a current of air is blown from an air blowing unit (a nozzle, or the like, and hereinafter, described as blower) 1 against an front end surface and side end surfaces of a paper bundle P, which is a plurality of papers stacked in a tray. This current of air sends air between the papers that make the paper bundle P. Accordingly, an uppermost paper P1 of the paper bundle P (hereinafter, referred to as uppermost paper) is floated to the height of a suction belt 2, and the uppermost paper P1 is sucked by the suction belt 2. Then, the sucked uppermost paper P1 is conveyed by the suction belt 2 to the image forming unit, and image formation is performed to the uppermost paper P1 in the image forming unit.
The blower 1 also handles the papers by blowing on a region in a predetermined height direction, and sending the air between the papers to float the papers. A paper damming up member 7 is arranged between the blower 1 and the paper bundle P, and prevents the papers other than the uppermost paper P1 from being conveyed. Further, a detection unit 3 that comes in contact with an upper surface of the uppermost paper P1 and detects the height of the paper bundle P is provided. The detection unit 3 detects data for constantly maintaining a distance h between the position of the uppermost paper P1 of the paper bundle P that is decreased due to passing of the papers and the suction belt 2. To realize that, an actuator 4 and a sensor 5 that detects swinging of the actuator 4, such as a photo sensor, are included. The actuator 4 swings due to a decrease of the papers, and the sensor 5 detects a moving amount of the swinging. A bottom plate 6 of a paper feeding tray 21 is lifted by a lift unit (not illustrated) or the like based on a detection signal thereof, and the position of the uppermost paper P1 of the paper bundle P is adjusted.
The papers that make the paper bundle P are stacked on the bottom plate 6 such that the front end surfaces are arranged as reference surfaces in accordance with the size of the papers, as illustrated in FIG. 1. A mounting position of the actuator 4 is a vicinity of a rear end of the paper bundle P, which is less subjected to an effect of the air blowing of the blower 1, as illustrated in FIG. 1. A conveyance roller 8 is arranged at a downstream side of the suction belt 2 in a paper conveying direction, and conveys the papers that have arrived. The conveying force of the conveyance roller 8 is set larger than the conveying force of the suction belt 2. Further, a paper feeding sensor 9 that detects arrival of a paper is provided at a downstream side of the conveyance roller 8 in the paper conveying direction.
Next, a paper feeding operation of the conventional paper feeding device illustrated in FIG. 1 will be described step by step.
(1) The blower 1 is actuated when a paper feeding instruction comes from a main body (not illustrated) of the image forming apparatus, and air blowing of the blower 1 to an end portion of the paper bundle P is started, as illustrated in FIG. 2. At the same time, air suction of the suction belt 2 is started. Accordingly, the uppermost paper P1 is floated, and the uppermost paper P1 is sucked to the suction belt, as illustrated in FIG. 2.
(2) Driving of the suction belt 2 and the conveyance roller 8 are started, and the paper P1 is conveyed (FIG. 3).
(3) The driving of the suction belt 2 is stopped after arrival of the paper P1 to the paper feeding sensor 9 (FIG. 4). The conveyance roller 8 continues conveyance of the paper P1 in a state where the suction belt 2 is being stopped.
(4) A paper P2 directly under the uppermost paper P1 is floated and sucked immediately after the paper P1 passes through a suction region (FIG. 5).
(5) The driving of the suction belt 2 is restarted, and the paper feeding of the paper P2 is performed, according to a set paper feeding interval.
(6) Hereinafter, the papers are sequentially conveyed from the paper bundle P by repetition of (2) to (5).
Next, behavior of the front end surface of the paper bundle P by air blowing will be described. Note that, in FIGS. 7(A) to 11(B), the arrow V in each drawing (B) illustrates each drawing (A) as viewed in a direction of the arrow V.
FIG. 6 is a detailed diagram of the blower 1. The air blowing unit 1 is divided into a floating nozzle 31 and a separating nozzle 32, and these nozzles have different functions. When air blowing is performed through the floating nozzle 31, air (31) blows into an upper portion of the paper P as illustrated in FIGS. 7(A) and 7(B), and floating and separation of the papers are performed at the same time. Among the floated papers, the uppermost paper is sucked by the suction belt 2, and is prepared for conveyance. Next, blowing through the separating nozzle 32 is performed from the state of FIGS. 7(A) and 7(B). The air blowing through the separating nozzle 32 is an air flow having a volume in an up and down direction. Therefore, the air blowing into a central portion of the papers is pressed in a downward direction except for the uppermost paper (FIGS. 8(A) and 8(B)). Accordingly, the papers are divided into the uppermost paper P1, and second and subsequent papers, and only the uppermost paper P1 sucked to the suction belt 2 is conveyed.
By the way, such a paper feeding device is required to perform paper feeding of a wide range of papers from a thin paper to a thick paper. In a paper feeding mechanism using the above air separation and suction, paper feeding of a thin paper may sometimes be difficult. When air blowing through the floating nozzle 31 is performed to thin papers set in the tray in the paper feeding mechanism using air separation and suction, floating of the papers can be easily performed because the papers are light. Accordingly, the second and subsequent papers are strongly pressed down to the suction belt 2, and the papers are closely adhered to the uppermost paper (FIGS. 9(A) and 9(B)). When the blowing through the separating nozzle 32 is performed in that state, the uppermost paper and the second paper are separated by the separation air in the central portion of the papers. However, the uppermost paper and the second paper other than the central portion remain to be closely adhered. When the paper feeding is performed in this state, the uppermost paper P1 and the second and subsequent papers are not completely separated, and thus, two papers may be conveyed while being stacked together. That is, double feeding occurs.
Therefore, there is a paper feeding device in which the paper damming up member 7 is arranged at a front surface of the paper feeding tray 21 (a surface of a downstream side in the paper conveying direction) in order to prevent the papers under the uppermost paper P1 from being drawn by the uppermost paper P1 and being fed (FIGS. 1, and 10(A) and 10(B)). The paper damming up member 7 is provided directly under the suction belt 2, and thus a clearance of about 1 to 3 mm is taken between the paper damming up member 7 and the suction belt 2 in order to prevent breakage of the suction belt 2. Therefore, the paper damming up member 7 is provided at a portion pressed by the separating nozzle 32 in a downward direction (in front of the separating nozzle), and exerts an effect to dam up only a pressed-down paper.
However, when the paper damming up member 7 is arranged in front of the separating nozzle 32, the flow of the air through the separating nozzle 32 is impeded (FIGS. 11(A) and 11(B)). Therefore, the pressing down effect by the separating nozzle 32 is decreased, and the papers under the uppermost paper P1 are slipped over the paper damming up member 7 and are fed. This causes occurrence of the double feeding. The occurrence of the double feeding causes wasteful consumption of the papers and inclusion of white papers in an output product, and significantly reduces the quality as a device.
In view of the above-described problems, there is a need to provide a paper feeding device capable of performing stable paper feeding and returning of a jammed paper to a paper feeding tray even in a paper feeding system using air separation and suction.